Anwendung des Agrarökosystemmodells EPIC zur Prognose des Wasser- und Nährstoffhaushaltes von landwirtschaftlich genutzten Flächen auf Sandböden in Ost-Brandenburg

Predictions of water and nutrient dynamics from agricultural sites on sandy soils in East- Brandenburg The validity of the agroecosystem model EPIC was tested for two agricultural sites on sandy soils without groundwater located at the moraine landscape in East-Brandenburg. Measurements of soil moisture, soil nitrate, above ground plant biomass and yield from these two agricultural investigation sites were compared with the corresponding simulation results of the model. The calculations of the soil water balance show a good fit between simulated and observed soil moisture values. The comparison between simulated and measured above ground plant biomass presents an underestimation of biomass by the model at the beginning of crop growth in spring and an overestimation at the end of the vegetation period. EPIC shows also an overestimation of yield in this study. The observed and the simulated soil nitrate values show no fit. Probably one reason for this fact might be the kind of process modeling included in EPIC, which was designed for long term calculations up to 50 years. Another possible reason could be the over estimation of N-uptakes of plants in comparison with estimates of the N-demand of plants based on the simulated yields. However a clear reason for the insufficient calculations of soil nitrate status by the model could not be found in this study. Further analysis of mineralization, N-uptake of plants and N-Ieaching in EPIC must be done in future.     

Root development of winter wheat in erosion‐affected soils depending on the position in a hummocky ground moraine soil landscape

Agricultural soil landscapes of hummocky ground moraines are characterized by 3D spatial patterns of soil types that result from profile modifications due to the combined effect of water and tillage erosion. We hypothesize that crops reflect such soil landscape patterns by increased or reduced plant and root growth. Root development may depend on the thickness and vertical sequence of soil horizons as well as on the structural development state of these horizons at different landscape positions. The hypotheses were tested using field data of the root density (RD) and the root lengths (RL) of winter wheat using the minirhizotron technique. We compared data from plots at the CarboZALF‐D site (NE Germany) that are representing a non‐eroded reference soil profile (Albic Luvisol) at a plateau position, a strongly eroded profile at steep slope (Calcaric Regosol), and a depositional profile at the footslope (Anocolluvic Regosol). At each of these plots, three Plexiglas access tubes were installed down to approx. 1.5 m soil depth. Root measurements were carried out during the growing season of winter wheat (September 2014–August 2015) on six dates. The root length density (RLD) and the root biomass density were derived from RD values assuming a mean specific root length of 100 m g^?1. Values of RD and RLD were highest for the Anocolluvic Regosol and lowest for the Calcaric Regosol. The maximum root penetration depth was lower in the Anocolluvic Regosol because of a relatively high and fluctuating water table at this landscape position. Results revealed positive relations between below‐ground (root) and above‐ground crop parameters (i.e., leaf area index, plant height, biomass, and yield) for the three soil types. Observed root densities and root lengths in soils at the three landscape positions corroborated the hypothesis that the root system was reflecting erosion‐induced soil profile modifications. Soil landscape position dependent root growth should be considered when attempting to quantify landscape scale water and element balances as well as agricultural productivity.     

Soil criteria for assessing the maximum permissible ground pressure of agricultural vehicles on Chernozem soils

The maximum permissible ground pressure of agricultural vehicles to permit satisfactory crop production on heavy loamy Chernozem soil was estimated from six criteria: (1) changes in soil water-physical properties; (2) crumbling characteristics; (3) depth of compaction; (4) rut depth; (5) soil strength potential; (6) self-loosening characteristics. Using these criteria it was possible to obtain reliable data for the maximum permissible ground pressure which was found to be correlated with the soil water content at the time of tillage.

At a water content equal to or somewhat lower than the water content at optimal soil crumbling (0.16–0.24 kg kg⁻¹), the permissible ground pressure was found to be within the range 80–120 kPa. At soil water contents slightly above the optimum soil crumbling (0.26–0.28 kg kg⁻¹), the permissible ground pressure was within the range 30–60 kPa.     

Productivity and nutrient use efficiency of maize,sorghum, and cotton in the West African Dry Savanna

Sustainable agricultural practices are needed to improve food security and support livelihoods in West Africa, where soil nutrient deficiencies and rainfed production systems prevail. The objective of this study was to assess the productivity and nitrogen (N) and phosphorus (P) use efficiencies of three dominant crops (maize, sorghum, and cotton) under different soil management strategies in the dry savanna of northern Benin. Data were collected for each crop in experiments with (1) an un‐amended soil as control, (2) a low use of external inputs, (3) an integrated soil–crop management practice, and (4) a high mineral fertilizer use, as treatments. Data were collected through researcher‐managed and farmer‐managed on‐farm trials in 2014 and 2015, and analyzed using linear robust mixed effects model and Pearson's correlation. Above‐ground biomass accumulation did not differ significantly among the control, integrated soil–crop management practice, and high mineral fertilizer use up to 30, 50, and 60 d after planting for maize, cotton, and sorghum, respectively. Thereafter, the differences in growth were substantial for each crop with highest biomass monitored with high mineral fertilizer use and lowest with the control. Biomass and economic yields at harvest were highest under high mineral fertilizer use and integrated soil–crop management practice, although the magnitude was crop‐specific. With the integrated soil–crop management practice and high mineral fertilizer use, N and P uptake by all crops was higher than for the un‐amended soil conditions. Inter‐seasonal changes in N uptake were higher for sorghum and cotton, but lower for maize. The highest agronomic efficiency and apparent recovery of N and P as well as positive N and P partial balances were obtained with the integrated soil–crop management practice for all three crops tested. The integrated soil–crop management strategy gave the highest yields and significantly improved N and P use efficiencies. The findings can contribute to formulating site and crop‐specific recommendations for sustainable agricultural practices in the Dry Savanna zone of West Africa.     

Parameter selection and testing the soil nitrogen dynamics model SOILN

Abstract. The SOILN model with a crop growth submodel for grass and cereal crops and the associated soil water and heat model SOIL were selected out of a number of similar models to simulate nitrogen cycling in a soil/crop system. The main parameter values required by the model were selected on the basis of a combination of field experiments and literature sources. Experimental data measured on grassland at Dumfries in the West of Scotland and on arable land at Bush Estate near Edinburgh were used to test the model. Simulated biomass yields and nitrogen contents of harvested biomass were in reasonable agreement with measured values for both grass and cereal crops. There were similar trends in accumulated leached nitrate between the simulations and experiments at the sites. Any discrepancy between simulated and measured nitrate leached appeared to correspond to similar discrepancies between simulated and measured water flow. The comparison between simulated and experimental results suggests that the model with the selected parameter values can simulate nitrogen and carbon cycling both in grassland and in arable land, and make convincing predictions about the effects of varying soil, crop, fertilizer and manure management practices. A basic sensitivity analysis carried out on the parameters determining the biological and biochemical processes showed the model predictions of annual N-leaching are relatively insensitive to all but two of the plant parameters. However, the model predictions of annual N-harvested and dry mass production are sensitive to numerous plant parameters.     

Analysis and simulation of soil organic‐carbon stocks in grassland ecosystems in SW Germany

Grassland extensification is followed by a change of soil organic‐matter (SOM) contents. In order to give a better assessment of these developments on grassland sites in SW Germany, the CENTURY Soil Organic Matter Model was used on five long‐term experimental sites under three different management practices (“Mowing”, “Mulching” (mowing without removal of the phytomass), and “Natural succession”). On these sites, soil‐organic‐carbon (SOC) monitoring was continuously done for soil depths of 0–4 and 4–8 cm from 1975 to 2002. The contents of organic carbon (OC) were at steady state or showed a slight decrease for the mulched and succession plots. Carbon contents of the mowed plots were decreasing. Measured C contents were transferred into stocks and compared with the simulated OC stocks. Linear regressions between observed and simulated C stocks were calculated separately for mulched and succession plots. The regressions for OC yielded significant relationships (R² = 0.8) for both kinds of plots. However, the model did not reproduce the short‐term dynamics of C stocks. Whereas SOC stocks on mulched and succession plots are expected to stay stable for the next decades according to the simulation, they are expected to decrease for a couple of years before stabilization on mowed plots.     

土壤水氮动态及作物生长耦合EPIC-Nitrogen2D模型

为计算农业区不同作物生长条件下土壤水氮迁移转化过程,该文基于Erosion/Productivity Impact Calculator(EPIC)作物模型建立了作物根系生长子模块,将其进行有限元数值离散,与土壤氮素迁移转化模型Nitrogen2D耦合,使模型能计算作物生长条件下土壤水氮迁移转化过程。该作物生长模块可计算多种胁迫下作物根系对土壤水分和氮素的动态吸收速率,及作物收获时的生物量和吸氮量。采用武汉大学灌溉排水试验场冬小麦生长条件下土壤水氮试验数据对模型进行了率定,并用于土壤水氮分布和作物生物量预测,土壤含水率、氮素的模拟值与实测值的一致性系数分别为0.86~0.97、0.52~0.98,Nash效率系数为0.59~0.90(含水率)、0.44~0.93(土壤氮素),说明模拟结果与实测值吻合度较高。同时,分别采用该文的作物生长模块和简单根系吸收模块计算根系吸氮过程,结果显示,简单根系吸收模型会显著高估作物吸氮量,而作物生长模型则由于考虑了根系生长和各环境因子的胁迫作用,计算结果更符合作物实际吸氮过程,计算的根系吸氮量相对均方根误差为3.4%~46%。     

基于SIMDualKc模型估算西北旱区冬小麦蒸散量及土壤蒸发量

为研究西北旱区冬小麦蒸散和土壤蒸发规律,以及土壤蒸发比例与其影响因子的关系,利用2 a冬小麦小区控水试验实测数据,对SIMDual Kc模型进行了参数校正和验证,对比大型称重式蒸渗仪的实测蒸散量值(或水量平衡法计算值)与模型模拟值。用建立的模型模拟精度评价标准对模拟值和实测值的误差进行评价。用经参数校验的模型模拟冬小麦农田土壤蒸发,并与微型蒸渗仪的实测值进行对比。基于通径分析方法研究气象因子(最低气温、最高气温、平均相对湿度、2 m处风速、太阳辐射量)和作物因子(地面覆盖度)与土壤蒸发比例的关系。结果表明,该研究建立的模型模拟精度评价标准能够较为全面地评价模型精度;SIMDual Kc模型可以较好地模拟西北旱区不同灌溉制度下冬小麦蒸散量和土壤蒸发量的变化过程,且在模拟长时段累积值时具有较高精度;拔节-灌浆期是冬小麦的需水关键期,冬小麦全生育期土壤蒸发比例呈现出生长中期生长后期快速生长后期生长初期的规律;灌水仅在短时间内影响土壤蒸发,地面覆盖度是影响土壤蒸发的最主要因子;在实测数据不充足的情况下,可以将地面覆盖度和蒸散量作为输入变量,用该研究确定的土壤蒸发比例与地面覆盖度的回归模型计算土壤蒸发量,该模型在计算不同水分条件下冬小麦农田土壤蒸发量时表现出较高的计算精度,决定系数在0.721~0.902之间,可以作为计算土壤蒸发量的简便方法。研究可为西北旱区冬小麦农田节水和灌溉决策提供理论依据。     

Infiltration patterns into two soils under conventional and conservation tillage: influence of the spatial distribution of plant root structures and soil animal activity

The characteristics and properties of the soil macropore system may cause different infiltration behavior under different tillage practices. To evaluate the effect of a specific tillage system on infiltration and percolation with particular regard to the influence of crop structure and soil animal activity dye tracer irrigation experiments were conducted in a silty (Luvisol) as well as in a sandy loam soil (Podzolluvisol). The spatial distribution of water flow paths was experimentally examined at four square areas of 0.49 m², under conservation and conventional tillage. Natural rainstorms were simulated by irrigating the plots with 2.8×10⁻³ M methylene blue solutions. For both soils the root crowns of the agricultural crop, wormcasts and stained soil sections as well as macroscopic conduits were traced on plastic sheets. The investigated soil depths were 0, 5, 10 and 20 cm for the both soils. For the Luvisol, the 30, 40, 50, 80 and 120 cm depths were also studied.For the Luvisol, the conservation tillage plot revealed pronounced vertical connectivity and continuity of the macropore network (maximum depth of stained pores=120 cm), while at the conventional tillage plot, continuous macropores were observed to soil depths of 50 cm, but mainly restricted to the ploughed topsoil (0–30 cm soil depth).For the Podzolluvisol, at the conservation tillage site extensive mulch residues prevented water transport beneath 5 cm soil depth. In contrast, at the conventionally tilled site stained water reached a depth of 20 cm. For all investigated plots on both soil types, the location of the root crowns of agricultural crop and of wormcasts was not related to percolation patterns.The results suggest that conservation tillage on silty soils under agricultural landuse could induce an increased water retention capacity reducing the significance of fast runoff components.     

黄土高原水土流失区干旱条件下节水灌溉持续增产效益诊断

针对黄土高原地区水资源的不合理利用而引发的一系列环境问题,水资源环境恶劣,农业生产条件受限,制约农业持续发展;人们的思想观念比较传统、陈旧、固守、落后,小规模经营;科学技术落后、信息不畅,区位劣势;生存环境失衡,水土流失严重,自然灾害频繁,作物产量低而不稳的现状,分析了节水灌溉和作物产量的关系,多角度探讨了地面节水灌溉、地上节水灌溉、地下节水灌溉三种不同形式,根据黄土高原水土流失区的实际情况,对旱作农业补充灌溉进行了研究。通过实地调查可知:节水灌溉已成为发展“两高一优”农业的有效途径和粮食再上新台阶的重要战略措施。     

Wheat growth and yield responses to biochar addition under Mediterranean climate conditions

The effects of the addition of a slow pyrolysis biochar (produced from olive-tree prunings) to a vertisol were studied in a field experiment during one wheat (Triticum durum L.) growing season. The biochar addition did not significantly affect soil parameters such as pH, dissolved organic C and N, ammonium, nitrate or microbial biomass N. By contrast, biochar addition decreased soil compaction and increased the soil water-retention capacity and nutrient content (total N and the available contents of P, K, Mg, Cu and Zn). These favourable changes led to an increase in fine root proliferation (increasing specific root length and reducing root tissue density) and promoted crop development. As a result, the plants in biochar-treated plots showed higher relative growth and net assimilation rates, aboveground biomass and yield than those in control plots. Neither grain quality nor nutrient content were significantly affected by biochar addition. Our results suggest that the use of biochar as a soil amendment in agricultural soils can improve soil physical properties and increase fertility, favouring crop development under semiarid Mediterranean conditions.     

Effects of irrigation and nitrogen fertilizer on yield,carbon inputs from above ground harvest residues and soil organic carbon contents of a sandy soil in Germany

To better understand the complex interactions between irrigation and nitrogen fertilizer application on soil organic carbon content, the results from long‐term field experiments over a period of 40 years were analysed. The combined effect of irrigation and nitrogen fertilizer rates on crop yields, carbon input by above ground harvest residues and soil organic carbon content has been investigated at a site on a sandy soil in northeast Germany. Combined with nitrogen fertilizer application, irrigation has frequently had a significantly positive effect on crop yield and carbon inputs from above ground harvest residues. However, enhanced carbon inputs to the soil under irrigation did not lead to significantly greater soil organic carbon contents. As the combination of irrigation and nitrogen also improved microbial decomposition by changing of above ground harvest residues C/N ratio and soil moisture, the effect of an additional input of carbon from above ground harvest residues was nullified.     

Of macropores and tillage: influence of biomass incorporation on cover crop decomposition and soil respiration

Carbon sequestration in agricultural soils may help to reduce global greenhouse gas concentrations, but building up soil carbon levels requires accumulating organic matter faster than it is lost via heterotrophic respiration. Using field and laboratory studies, this study sought to elucidate how tillage, the below‐ground incorporation of cover crop residue, and soil macroporosity affect soil respiration and residue decomposition rates. In the field, residue from a cover crop mixture of barley (Hordeum vulgare ) and crimson clover (Trifolium incarnatum ) was placed into litter bags that were left on the surface versus incorporated into the soil at three depths (4, 8 or 12 cm), while the laboratory study compared surface‐placed versus incorporated litter (8 cm depth). To assess tillage effects on cover crop decomposition, the field study simulated no‐till and conventional tillage treatments, while the laboratory and field studies both included treatments in which artificial soil macropores were created. The field study showed that conventional tillage and the presence of macropores enhanced soil respiration, while in the laboratory study, incorporating cover crop residue resulted in higher soil respiration and faster litter decomposition rates. Additionally, the laboratory measurements showed that macropores increased soil respiration in wet conditions, likely by enhancing oxygen diffusion. Thus, organic matter incorporation and macropores may represent important factors that affect soil respiration and carbon dynamics.     

The influence of soil and biosolids type,and microbial immobilisation on nitrogen availability in biosolids‐amended agricultural soils – implications for fertiliser recommendations

Soil microbial biomass interactions influencing the mineralisation of N in biosolids‐amended agricultural soil were investigated under field conditions in two soil types, a silty clay and a sandy silt loam, with contrasting organic matter contents. Soil treatments included: dewatered raw sludge (DRAW); dewatered and thermally dried, mesophilic anaerobically digested biosolids (DMAD and TDMAD, respectively); lime‐treated unstabilised sludge cake (LC); and NH₄Cl as a mineral salt control for measuring nitrification kinetics. Soil mineral N and microbial biomass N (MBN) concentrations were determined over 90 days following soil amendment. Despite its lower total and mineral N contents, TDMAD had a larger mineralisable pool of N than DMAD, and was an effective rapid release N source. Increased rates of mineralisation and nitrification of biosolids‐N were observed in the silty clay soil with larger organic matter content, implying increased microbial turnover of N in this soil type compared with the sandy silt loam, but no significant difference in microbial immobilisation of biosolids‐N was observed between the two soil types. Thus, despite initial differences observed in the rates of N mineralisation, the overall extent of N release for the different biosolids tested was similar in both soil types. Therefore, the results suggest that fertiliser guidelines probably do not need to consider the effect of soil type on the release of mineral N for crop uptake from different biosolids products applied to temperate agricultural soils.     

Long‐term effects of tillage,nutrient application and crop rotation on soil organic matter quality assessed by NMR spectroscopy

Crop and land management practices affect both the quality and quantity of soil organic matter (SOM) and hence are driving forces for soil organic carbon (SOC) sequestration. The objective of this study was to assess the long‐term effects of tillage, fertilizer application and crop rotation on SOC in an agricultural area of southern Norway, where a soil fertility and crop rotation experiment was initiated in 1953 and a second experiment on tillage practices was initiated in 1983. The first experiment comprised 6‐yr crop rotations with cereals only and 2‐yr cereal and 4‐yr grass rotations with recommended (base) and more than the recommended (above base) fertilizer application rates; the second experiment dealt with autumn‐ploughed (conventional‐till) plots and direct‐drilled plots (no‐till). Soil samples at 0–10 and 10–30 cm depths were collected in autumn 2009 and analysed for their C and N contents. The quality of SOM in the top layer was determined by ¹³C solid‐state NMR spectroscopy. The SOC stock did not differ significantly because of rotation or fertilizer application types, even after 56 yr. However, the no‐till system showed a significantly higher SOC stock than the conventional‐till system at the 0–10 cm depth after the 26 yr of experiment, but it was not significantly different at the 10–30 cm depth. In terms of quality, SOM was found to differ by tillage type, rate of fertilizer application and crop rotation. The no‐till system showed an abundance of O‐alkyl C, while conventional‐till system indicated an apparently indirect enrichment in alkyl C, suggesting a more advanced stage of SOM decomposition. The long‐term quantitative and qualitative effects on SOM suggest that adopting a no‐tillage system and including grass in crop rotation and farmyard manure in fertilizer application may contribute to preserve soil fertility and mitigate climate change.     

Effects of agricultural practices on hydraulic properties and water movement in soils in Brittany (France)

The intensive agricultural use of soils in the Brittany region (western France) has increased the need for a better understanding of soil water dynamics. The aim of the present study is to compare quantitatively the differences produced by two agricultural practices on soil hydraulic properties (water retention curve and hydraulic conductivity) as well as the infiltration and drainage fluxes in the soils. This study was carried out on two experimental plots managed in the same way for 22 years. The two practices were continuous maize fertilized with mineral fertilizer, denoted as MX, and pasture within a ray-grass/maize rotation (3/1 year) with organic fertilization (pig slurry), denoted as PR. The study consisted of measuring soil physical properties in the laboratory and in the field, and estimating water infiltration in the soil of the two plots by recording water pressure heads after simulation of 2-h artificial rainfall with an intensity of 17 mm/h. We applied the van Genuchten model to describe the water retention and hydraulic conductivity curves (θ(h) and K(h)) for each soil horizon of the two plots. Hydrus-2D and ID softwares were used to construct a numerical model of water movement in the two soils. This model was used to quantify the infiltration rate, deep drainage and actual evaporation fluxes during the artificial rainfall experiment.The vertical influence of agricultural practices in both plots appears to be limited to the uppermost 35 cm. Deeper in the B horizon, there are only very slight differences in the hydraulic properties between the two plots. In the top soil horizons (H1–H5 and H6), the two soil properties mostly affected by practices are the hydraulic conductivity and the α parameter of the van Genuchten model. At the lowest pressure head studied here (−1.5 kPa), hydraulic conductivity in a given horizon differs by more than one order of magnitude between the two plots. The model reproduces quite satisfactorily the observed pressure heads in plot PR at all depths, in the rainy period as well as in the water redistribution period (efficiency >0.77). Results are less good for the MX plot, with efficiency ranging from 0.49 to 0.84 depending on the horizon. The different sources of simulation errors are identified and discussed. For the MX plot, the soil water movement model succeeds in reproducing the infiltration excess runoff observed in the field, allowing us to calculate that it accounts for 9% of the applied rainfall. No surface runoff or ponding appears in the PR plot during the artificial rainfall experiment. In the PR plot, the simulated deep drainage flux increases more rapidly than in the MX plot. The lower hydraulic conductivity in the top soil horizon of the MX plot compared with the PR plot appears to reduce the infiltration rate as well as the deep drainage flux. It also decreases the upward flow of water to the soil surface when the water content in the top soil layer is depleted by evaporation flux. The model simulation could be improved by a more precise representation of the soil structure, particularly the location, size and frequency of clods as well as the variability of hydraulic properties. However, we need to strike a balance between improving the quality of the simulation even further and the practical constraints and efforts involved in measuring the soil hydraulic properties.     

分形模型在利用颗粒分布数据评价土壤持水性质中的应用

Soil water retention characteristics are the key information required in hydrological modeling.Frac-tal models provide a practical alternative for indirectly estimating soil water retention characteristics from particle-size distribution data.Predictive capabilities of three fractal models,i.c.,Tylcr-Wheatcraft model,Rieu-Sposito model,and Brooks-Corey model,were fully evaluated in this work using experimental data from an international database and literature.Particle-size distribution data were firstly interpolated into 20 classes using a van Genuchten-type equation.Fractal dimensions of the tortuous pore wall and the pore surface were then calculated from the detailed particle-size distribution and incorporated as a parameter in fractal water retention models.Comparisons between measured and model-estimated water retention cha-racteristics indicated that these three models were applicable to relatively different soil textures and pressure head ranges.Tyler-Whcatcraft and Brooks-Corey models led to reasonable agreements for both coarse-and medium-textured soils,while the latter showed applicability to a broader texture range.In contrast,Rieu-Sposito model was more suitable for fine-textured soils.Fractal models produced a better estimation of water contents at low pressure heads than at high pressure heads.     

Effects of biochars produced from different feedstocks on soil properties and sunflower growth

The use of biochar as a soil amendment is gaining interest to mitigate climate change and improve soil fertility and crop productivity. However, studies to date show a great variability in the results depending on raw materials and pyrolysis conditions, soil characteristics, and plant species. In this study, we evaluated the effects of biochars produced from five agricultural and forestry wastes on the properties of an organic‐C‐poor, slightly acidic, and loamy sand soil and on sunflower (Helianthus annuus L.) growth. The addition of biochar, especially at high application rates, decreased soil bulk density and increased soil field capacity, which should impact positively on plant growth and water economy. Furthermore, biochar addition to soil increased dissolved organic C (wheat‐straw and olive‐tree‐pruning biochars), available P (wheat‐straw biochar), and seed germination, and decreased soil nitrate concentration in all cases. The effects of biochar addition on plant dry biomass were greatly dependent upon the biochar‐application rate and biochar type, mainly associated to its nutrient content due to the low fertility of the soil used. As a result, the addition of ash‐rich biochars (produced from wheat straw and olive‐tree pruning) increased total plant dry biomass. On the other hand, the addition of biochar increased the leaf biomass allocation and decreased the stem biomass allocation. Therefore, biochar can improve soil properties and increase crop production with a consequent benefit to agriculture. However, the use of biochar as an amendment to agricultural soils should take into account its high heterogeneity, particularly in terms of nutrient availability.     

Incorporation of catch crop residues does not increase phosphorus leaching: a soil column experiment in unsaturated conditions

Some studies suggest that incorporation of catch crop residues leads to increased availability of P to plants. However, little information is available on how this affects P leaching in soils with a high P load. We tested the effect of catch‐crop residue incorporation at the end of winter on the P leaching potential in a soil column experiment under unsaturated conditions using a typical sandy loam soil of NW Europe characterized by a high P load. We sampled the catch crops white mustard (Sinapis alba L.), Italian ryegrass (Lolium multiflorum L.), black oats (Avena strigosa L.) and a perennial ryegrass‐white clover mix (Lolium perenne L.‐Trifolium repens L.) from a field trial on catch crops and soil from the plots where they were grown. Plant biomass was incorporated taking account of the differences in conditions of the plant material at the end of winter and the biomass yield of each catch crop. Incorporation of catch‐crop residues decreased P leaching compared to the fallow treatment probably through immobilization of soil P during catch crop residue decomposition. The exception was black oats, where the leaching of P was the same as for fallow soil. We observed clear differences in C/N, C/P, water soluble and total P concentration, and biodegradability between the tested catch crops, which seemed to affect the P leaching. We conclude that the incorporation of catch crop residues under typical soil and weather conditions and agricultural practices of NW Europe does not increase the potential P leaching losses.